The present disclosure relates to harvesting articulated (jointed) combines and more particularly to an articulated combine design that permits additional sieve capacity concomitant with tailings return thereto.
Typical to the architecture of traditional combines are cleaning sieves that are located to the rear of and beneath the threshing mechanisms of the combine harvester. This routinely results in the sieves being located between both and/or one of the two sets of tires typical to these machines—large front tires and smaller rear steering tires. As such, the width of the sieves is regulated by the distance between these respective sets of tires and especially the smaller rear steering tires. In the case of the large front tires, they have a fixed orientation relative to the length of the machine, and generally are held fast, parallel to the chassis containing the threshing and cleaning mechanisms.
However, in the case of the rear steering tires, they effect the steering by rotating around their (more or less) vertical king pin, and in so doing move considerably inwardly toward the side of the machine either in their front or their rear depending on the direction of steering. This inward movement of the steered tires necessitates a corresponding reduction in the width of the separator to allow tire clearance. And, then, as the rear axle oscillates around its central pivot pin allowing the tires to move up and down literally feet in distance, the tires move inwardly even more. All of this describes why the width of sieves in a typical combine often are reduced to a width that is much less than adequate for the given capacity of a high horsepower modern combine resulting in lower than desired cleaning system capacity of the machine. It is literally not feasible to raise the sieves high enough to accommodate the axle oscillation if one desires to make the sieves wider near the rear of the machine.
Therefore, it is nearly mandated that if a manufacturer wishes to add addition sieve area, he cannot do it by adding sieve width, which is quite effective, but instead must choose to keep the sieves the same width and just make them longer, which is much less effective.
Combine designers realized at the outset that they needed to recover unthreshed material as it exited from the rear of the sieves and return it to the threshing mechanism for rethreshing to separate additional grain from the MOG. This was an acceptable practice when harvesting combine machines were small and rotary threshing capacity was not challenged.
As combine horsepower and capacities have increased over time, the industry has learned not to return the tailings to the front of the rotor for reprocessing, and has instead learned to reprocess the tailings near the rear of the separator and return them to the upper sieve for recovery of the grain. The crux of this issue is explained as follows: if the rotor is running very near its maximum capacity to thresh and separate the volume of material the feeder is providing, then the rotor cannot effectively address separating at the increased rate that recycling tailings would require. That is, the best that the rotor can do is to recover grain without tailings return. With an increased burden caused by tailings recycle, the rotor necessarily is beyond its maximum capacity and the percentage of grain recovered diminishes. That means that the amount of tailings to recycle will increase. This is a spiraling diminution in grain recovery. Thus, a different approach to the issue of tailings recycle is required.
Fortuitously, inherent in the design of articulated combines is the ability to provide a second grain cleaning station (so-called “bonus sieves” herein), which can additionally address and solve the tailings recycle issue.